A boat's speed in still water is 45 km/h, while the river is flowing at a speed of 15 km/h. The time taken to cover a certain distance upstream is 9 h more than the time taken to cover the same distance downstream. Find the distance (in km).

Given: ​

Speed of boat in still water = 45 km/h 

Speed of the current = 15 km/h

Time taken by upstream is 9 hours more than time taken by downstream.

Formula Used: ​

Downstream speed = speed of boat + speed of current

Upstream speed = speed of boat - speed of current

Distance = $$Speed \times time$$ 

As per the question;

Downstream speed of boat = 45 + 15 = 60 km/h

Upstream speed of boat = 45 - 15 = 30 km/h

Let the Distance be D then,

​$$\frac{D}{30}-\frac{D}{60} = 9$$ 

​$$\frac{2D-D}{60} = 9$$ 

$$\frac{D}{60}=9$$ 

D = 540 km

(u +v) : (u – v) = 60 : 30 = 2 : 1
Ratio of time = 1 : 2
Difference = 2 - 1 = 9h
Distance = 60 × 9 = 540 km ​​